1. Field of the Invention
The present invention relates to bidirectional optical burst transmission through an optical fiber and, more particularly, to a signal discrimination method and apparatus for ensuring reliable discrimination of signal light in optical burst transmission even when reflected light and signal light occur close to each other or are superimposed one on top of the other.
2. Description of the Related Art
In recent years, due to an ever increasing amount of information transmission, the need for inexpensive optical transmission systems has been increasing, particularly in the case of subscriber optical transmission systems. Under these circumstances, there have been developed systems for performing bidirectional optical burst transmission using a single optical fiber and bidirectional optical burst transmission systems for one-to-many bidirectional communication.
In such bidirectional optical burst transmission, if reflected light that returns immediately after the transmission of an optical signal occurs close to the signal light transmitted from the other station, or is superimposed on it, it may become difficult to discriminate the signal light since the reflected light and the signal light are received as continuous data. This problem can occur even in wavelength-division multiplexed transmission where different transmission wavelengths are assigned to different stations, if the separation between different wavelengths is not sufficient.
To prevent overlapping or collision between reflected light and signal light, it has been commonly practiced to suppress the reflected light below the receivable level or to provide a reflection guard time for eliminating the interference between the reflected light and the signal light.
To suppress reflected light, the level of the reflected light needs to be suppressed below the light OFF detection level, which necessitates decreasing the reflected light level by applying advanced physical contact (APC) or angled polishing to fiber ends in an optical connector, or raising the light OFF detection level though this degrades the reception level. This necessarily leads to a cost increase and performance degradation.
On the other hand, the guard time method involves the problem of degrading information transmission efficiency since signal transmission cannot be performed during the guard time.